Process for the recovery of polyglycerols from distillation residues



United States Patent Q a l.

PROCESS FOR THE RECOVERY OF POLYGLYC- EROLS FROM DISTILLATION RESIDUES Richard Rowe, Altrincham, England, assignor to Victor Wolf Limited, Manchester, England No Drawing. Application June 6, 1950,

Serial No. 166,537

Claims priority, application Great Britain June 14, 1949 6 Claims. (Cl. 260-616) This invention relates to a new or improved process for the recovery of polyglycerols from the residues remaining from the distillation of crude glycerine. These residues are known as glycerine pitch or glycerine foots.

The glycerine pitch remaining from the distillation of crude glycerine consists mainly of polyglycerols together with some glycerine not removed by distillation and, in the case of glycerine from soap lyes, common salt. More over it contains other inorganic salts, soap and salts of organic acids other than soap acids. Accordingly, on ignition of glycerine pitch there is a substantial ash residue often amounting, even in the case ofsaponification glycerine, to from 10 to which is referred to as the ash content.

The principal object of the present invention is to enable polyglycerols of very low ash content, i. e., so low as to be negligible, to be recovered from such glycerine pitch. So far as we are aware, this object has never been satisfactorily achieved by any method of extraction. In the presence of polyvalent alcohols the solvents which dissolve polyglycerols easily, such as the lower aliphatic alcohols, readily dissolve the organic salts contained in the glycerine pitch and thus practically all the ash-forming ingredients are obtained in the extract. Attempts have been made to use solvents such as acetone or ethyl acetate for the extraction but these are not good solvents for polyglycerols even at their boiling point and the polyglycerol which they extract still generally contains 1% or more of ash.

One object of the present invention is to obtain polyglycerols having a negligible ash content, i. e., below 1%, and mostly below 0.5%. Another object of the invention is to obtain polyglycerols having an ash content below 0.1%.

These objects are secured by obtaining polyglycerols from glycerine pitch by solvent extraction, employing dioxane as the solvent.

Dioxane has been found to dissolve polyglycerols to a useful extent even at room temperature and at its boiling point seems to be miscible in all proportions with polyglycerols. On the other hand, the salts contained in glycerine pitch, even the salts of organic acids, are almost insoluble in dioxane.

In one form of the present invention polyglycerols, together with any glycerine which may be present, are extracted from glycerine pitch by treatment of the pitch with dioxane, separation of the dioxane solution from undissolved materials and distillation of the dioxane. The extraction is preferably carried out with hot dioxane, the dioxanesolution being separated from the residue before any substantial cooling has taken place.

A convenient procedure is to treat glycerine pitch with hot dioxane, separate the resulting solution of polyglycerols in dioxane while hot from undissolved materials, cool the solution in stages to effect fractional separation of the polyglycerols from the solution and remove the fractions thus separated from the remaining solution. By thus cooling the dioxane solution in stages the poly- 2,717,271 Patented Sept. 6, 1955 ICC glycerols which first come out of solution are more highly polymerised than those which come out later or which remain in the cooled solution. By changing the concentration of the extract from which the polyglycerols are separated by cooling, the composition of the fractions which so separate can be influenced. It is quite useful simply to obtain two fractions, one by cooling the'hot solutionand by drying the product which separatesout and the other by evaporating the dioxane from the remaining cooled solution; cooling can be effected to room temperature.

If desired, the pitch can be purified before extraction, by anyof the known methods. In the case of pitches obtained from glycerine resulting from the manufacture of soap it is particularly useful to remove the greater part of the salt which is present.

Instead of treating the pitch itself I may treat a crude extract'of polyglycerols therefrom, e. g., an extract obtained by the use of aliphatic alcohols having from 3 to v 5 carbon atoms in the molecule.

By such a preliminary extraction with an aliphatic alcohol'a product of fairly low ash content can be obtained from which a product of negligible ash content can in turn be extracted by means of dioxane.

In carrying out the invention the glycerine pitch or crude polyglycerol can be simply boiled with dioxane pref erably with stirring, then the hot dioxane solution separated from the residue. The dioxane is then distilled off, with or Without cooling and fractional separation of more highly polymerised polyglycerols. Alternatively the extraction can be made by first distributing the pitch or crude polyglycerol over a large area of surface before extraction with dioxane. For example, hot glycerinepitch may be mixed with particulate material having a large surface area which may be of fibrous or granular character, such as sawdust, alumina or silica gel, before extraction. Such distribution of glycerine pitch on adsorbent substances or substances having large surface area has been already proposed in a process in which the extraction was carried out with an organic solvent such as acetone, ethyl acetate or a low boiling alcohol. I have found, however, that such organic solvents do not bring about a satisfactory extraction nor yield polyglycerols of satisfactory low ash content.

The amount of dioxane used should be sufficient to enable the solution of polyglycerols to be conveniently separated from the undissolved matter. The most suitable amount in any particular case will depend upon a number of factors, e. g., whether the extraction is by a continuous or batch process, whether the glycerine pitch is mixed with a particulate material such as sawdust and whether the extraction is effected at the boiling point or at a lower temperature; it also depends upon the nature of the glycerine pitch to be treated. Generally, it is most convenient to extract at the boiling point and in a batch process this will usually require the use of an amount of dioxane more than the weight of the polyglycerol-containing material and it has been found that substantially three times the weight of the polyglycerol-containing material ismost convenient. In a continuous process, substantially smaller amounts of solvent can be used, for example, a weight equal to the weight of polyglycerolcontaining material.

Example 1 parts by weight of glycerine pitch remaining from the distillation of crude glycerine from a saponification process are boiled with 300 parts by weight of dioxane for several hours while stirring vigorously to make the hard sticky pitch more accessible to the action of the solvent. The hot solution is finally separated from the residue and the dioxane distilled off. The resulting extract is a clear 3 viscous liquid with a hydroxyl value of 851 and an ash content of 0.05%.

Example 2 Glycerine pitch is mixed while hot with 1 /2 times its weight of sawdust which has previously been extracted with dioxane until a substantially uniform mixture has been obtained. This mixture is then extracted with dioxane at a temperature of 60 to 70 C. After completion of the extraction the dioxane is removed by evaporation. The resulting extract is a viscous liquid of hydroxyl value 980 and has an ash content of 0.01%. It can be freed from some water-insoluble impurities by dissolving it in water, filtering the solution and evaporating it.

In Example 2 a temperature of 60 to 70 C. is employed. However, any temperatures within the range of about 50 to 80 C. are quite satisfactory. Higher temperatures are not necessary in the case where the pitch is mixed with a solid substance but on the other hand the extraction is rather slow at temperatures below about 50 C.

To facilitate mixing with the sawdust, the pitch may first be dissolved in a solvent such as Water or methanol; this solvent must be removed from the mixture, e. g. by evaporation, before extraction with dioxane.

It will be appreciated that the extracts obtained with the aid of dioxane according to the present invention do not consist solely of polyglycerols. They consist of products composed substantially of polyglycerols but having a very low ash content.

I claim:

1. Process for obtaining polyglycerols of low ash content from glycerine pitch containing salts of organic acids which comprises treating said pitch with dioxane to dissolve said polyglycerols, separating the resulting solution of polyglycerols in dioxane from undissolved materials and removing the dioxane from said solution by distillation.

2. Process for obtaining polyglycerols of low ash content from glycerine pitch containing salts of organic acids which comprises treating said pitch with hot dioxane to dissolve said polyglycerols, separating the resulting hot solution of polyglycerols in dioxane from undissolved materials and removing the dioxane from said solution by distillation.

3. Process for obtaining polyglycerols of low ash content from glycerine pitch containing salts of organic acids which comprises treating said pitch with hot dioxane to dissolve said polyglycerols, separating the resulting hot solution of polyglycerols in dioxane from undissolved materials, cooling said solution to cause some dissolved polyglycerols to come out of solution, separating the resulting cooled solution from such polyglycerols and removing the dioxane from said cooled solution by distillatron.

4. in a process for obtaining polyglycerols from glycerine pitch containing salts of organic acids by solvent extraction, the employment of dioxane as a solvent.

5. Process for obtaining polyglycerols of low ash content from crude polyglycerol of higher ash content extracted from glycerine pitch containing salts of organic acids which comprises treating said crude polyglycerols with dioxane to form a polyglycerol solution of low ash content, separating said solution from undissolved materials and removing the dioxane from said solution by distillation.

6. Process for obtaining polyglycerols of low ash content from glycerine pitch containing salts of organic acids which comprises treating said pitch with hot dioxane to dissolve said polyglycerols, separating the resulting hot solution of poiyglycerols in dioxane from undissolved matcrials, cooling said solution in stages to effect fractional separation of the polyglycerols from the solution and removing the fractions thus separated fromthe remaining solution.

References Cited in the tile of this patent UNiTED STATES PATENTS 1,278,023 Rosenbaurn Sept. 3, 1918 1,509,325 Weir et al. Sept. 23, 1924 2,056,830 Coleman et a1. Oct. 6, 1936 2,233,606 Hass Mar. 4, 1941 2,325,379 Durrum July 27, 1943 2,357,344 Morris et a1 Sept. 5, 1944 2,382,764 Young et al Aug. 14, 1945 2,436,209 Elgin Feb. 17, 1948 2,444,296 Keim et al. June 29, 1948 2,444,582 Smith July 6, 1948 2,461,220 Lorano Feb. 8, 1949 2,477,551 Wittcoif July 26, 1949 2,479,041 Elgin Aug. 16, 1949 FOREIGN PATENTS 245,098 Great Britain Dec. 23, 1924 OTHER REFERENCES Reid et al., Ind. 86 Eng. Chem, vol. 21, pages 695-697 Jordan, The Technology of Solvents (1937), Leonard Hill Ltd., London, page 273. 

4. IN A PROCESS FOR OBTAINING POLYGLYCEROLS FROM GLYCERINE PITCH CONTAINING SALTS OF ORGANIC ACIDS BY SOLVENT EXTRACTION, THE EMPLOYMENT OF DIOXIDE AS A SOLVENT. 